1. Field of the Invention
The invention relates to an ink-droplet ejecting apparatus of inkjet type.
2. Description of Related Art
An inkjet printer as a kind of ink-droplet ejecting apparatus includes an inkjet head having an ink passage including a pressure chamber and ending at a nozzle, and an actuator which may be of piezoelectric type. The actuator is applied with a drive signal in the form of pulses to be displaced or deformed thereby, in order to apply a pressure to ink in the pressure chamber to eject a droplet of the ink from the nozzle.
It is known to damp a pulsation remaining in the ink after the ejection of an ink droplet, or to reduce the size or volume of an ink droplet to be ejected, by adding a pulse Ps that is not for ejecting an ink droplet, to the drive pulse. More specifically, the drive pulse includes a main pulse Pm that is for ejecting an ink droplet, and the pulse Ps is applied after the main pulse Pm.
For instance, JP-A-2001-301161 (see especially FIG. 1), which is publication of a patent application by the present applicant, discloses to first apply a main pulse for ejecting an ink droplet, and then apply a non-ejection pulse or stabilizing pulse not for ejecting an ink droplet. In the technique of the above-mentioned publication, a waveform of the drive signal is changed depending on whether it is instructed to eject an ink droplet immediately before or after a specific ink droplet or dot. When such an instruction is not issued, a first waveform is employed, and when the instruction is issued, a second waveform is employed. The first waveform is such that where a time taken by a pressure wave occurring in a pressure chamber to propagate one way along an ink passage is represented by AL, a pulse width of the main pulse is 1.0AL and the stabilizing pulse having a pulse width of 0.2AL-0.3AL is applied after an interval of 0.4AL-0.6AL from the main pulse. The second waveform is such that the pulse width of the main pulse is 0.5-0.7AL and the non-ejection pulse having a pulse width of 0.2AL-0.3AL is applied after an interval of 2.0AL-2.2AL from the main pulse. It is noted that in the above-mentioned publication, the one-way propagation time AL is denoted by T.